The present invention relates to tracked vehicle systems and more particularly concerns a vehicle system embodying a track guideway that has an upwardly convex transverse curvature.
Tracked vehicle systems generally embody a track structure including spaced rails particularly configured for support of vehicle wheels or other levitation arrangements. Magnetic levitation has been widely suggested, though less widely employed, for systems in which speeds may exceed those that are conveniently or safely attainable for wheeled vehicles. Particularly for high speed inter-city public transportation, magnetic levitation systems of various designs and configurations continue to be proposed. High speed trains provide advantages of easing overcrowded freeways and airports, reduction of pollution and facilitating mass transportation of riders between congested urban centers. Despite the many advantages of proposed high speed transport systems, few such proposals have been adopted. Among obstacles to widespread adoption of high speed transport systems are the track configuration, and, in particular, track system costs. Track configuration cross sections frequently include planes and surfaces for magnetic levitation extending in different directions, requiring complex structures needed to provide both lateral and vertical support. High speed magnetically levitated vehicle systems presently require high precision of track configuration and position, thereby greatly increasing cost of construction and maintenance. Such tracks must be carefully leveled and aligned, both longitudinally and transversely, often to small fractions of an inch.
Banking of such track structures at curved track sections is essential and becomes ever more important as speeds increase. As the vehicle travels along a curved track section, optimum lateral stability is achieved when the resultant of gravitational and centrifugal acceleration forces is perpendicular to the track surface. The direction of such resultant depends upon track curvature and vehicle speed, and thus, for a track of given curvature, the track has an optimum bank angle for any one speed. In present systems this bank angle is fixed when the track is constructed, and thus, for optimum operation, the vehicle must traverse such a banked curved section at a single predetermined speed. This may cause difficulties for a vehicle normally programmed for high speed operation on a track banked for such speed. Under certain circumstances the vehicle may be required to traverse a high speed curved section at a lower speed, or in some cases to stop at such section. In such a situation, not only is the tilt of the vehicle objectionable to passengers and freight, but it may increase the tendency of the vehicle to overturn, toward the inside of the curve. On the other hand, if the vehicle should run at too high a speed along a curve having too small a bank angle, centrifugal force becomes too large for the amount of bank and tends to laterally displace the vehicle outwardly of the curved track. Such forces, which can create dangerous situations, become of greater concern as vehicle speeds increase.
With a fixed bank angle, the track cannot properly handle both high speed passenger trains and slow, heavily laden freight trains. If the track curves are banked for high speed the heavy freight train may be required to traverse such curves at a speed higher than optimum, thus paying an economic penalty in fuel costs to overcome increased drag at the higher speeds.
Accordingly, it is an object of the present invention to provide a tracked vehicle system in which above-mentioned problems are avoided or minimized.